The prior art particularly comprises documents U.S. Publication No. 2010/021295A1, U.S. Publication No. 2004/042897A1, French Publication No. 2945680A1, French Publication No. 2994707, and U.S. Publication No. 2010/310368A1.
A turboprop engine comprises at least one propeller comprising a hub and blades supported by the hub and extending substantially radially outwards relative to the hub and to the axis of rotation of the propeller.
The turboprop engine is generally equipped with a propeller pitch actuation system, also called a propeller blade angular pitch system. Adjusting the pitch of the propeller blades allows their efficiency to be improved while guaranteeing a propeller rotational speed for each flight phase.
Each blade can be rotated about an axis, which is generally radial, between a first emergency position, called the feathering position, in which it extends substantially parallel to the axis of rotation of the propeller, and a second position, in which it is sharply inclined relative to this axis. It can adopt any position between these two extreme positions.
In the prior art, the actuation system that is used is a hydraulic system, which is relatively complex and has several disadvantages. This system comprises an actuator, a movable part of which is connected to the propeller blades so as to adjust their pitch.
The actuation system must be able to provide not only the pitch control function, but also the emergency blade feathering function. The pitch actuation system thus comprises an auxiliary system for the emergency function.
A malfunction associated with a leak in the hydraulic system, which is a mode common to the pitch control system and the auxiliary system, must be covered. Without a pressure source, it is essential that counterweights are added to the blades in order to provide the feathering function.
The pitch actuation system also must provide protection functions in the event of overspeed, in the event of engine cut-out, in the event of a failure of the FADEC (Full Authority Digital Engine Control) computer, and must ensure that low pitches in flight are limited. A set of mechanical systems and of hydraulic systems thus form part of the pitch actuation system for providing these functions in the prior art.
The pitch control system is also subject to extremely strict malfunction rate requirements, which involve redundancies and additional protection systems.
To conclude, the technology and the operating principle of a hydraulic propeller pitch actuation system are currently complex. These systems are integrated in a wide range of hydraulic components.